The archetype ionic transition‐metal complexes (iTMCs) [Ir(ppy)2(bpy)][PF6] and [Ir(ppy)2(phen)][PF6], where Hppy = 2‐phenylpyridine, bpy = 2,2′‐bipyridine, and phen = 1,10‐phenanthroline, are used as the primary active components in light‐emitting electrochemical cells (LECs). Solution and solid‐state photophysical properties are reported for both complexes and are interpreted with the help of density functional theory calculations. LEC devices based on these archetype complexes exhibit long turn‐on times (70 and 160 h, respectively) and low external quantum efficiencies (∼2%) when the complex is used as a pure film. The long turn‐on times are attributed to the low mobility of the counterions. The performance of the devices dramatically improves when small amounts of ionic liquids (ILs) are added to the Ir‐iTMC: the turn‐on time improves drastically (from hours to minutes) and the device current and power efficiency increase by almost one order of magnitude. However, the improvement of the turn‐on time is unfortunately accompanied by a decrease in the stability of the device from 700 h to a few hours. After a careful study of the Ir‐iTMC:IL molar ratios, an optimum between turn‐on time and stability is found at a ratio of 4:1. The performance of the optimized devices using these rather simple complexes is among the best reported to date. This holds great promise for devices that use specially‐designed iTMCs and demonstrates the prospect for LECs as low‐cost light sources.
Dye-sensitized solar cells with carboxylate-derivatized {Cu(I)L(2)} complexes are surprisingly efficient and offer a long-term alternative approach to ruthenium-functionalized systems.
Light‐emitting electrochemical cells with lifetimes surpassing 3000 hours at an average luminance of 200 cd m−2 are obtained with an ionic iridium(III) complex conveniently designed to form a supramolecularly caged structure.
Light-emitting electrochemical cells (LECs) containing [Cu(POP)(N^N)][PF6] (POP = bis(2-diphenylphosphinophenyl)ether, N^N = 6-methyl- or 6,6'-dimethyl-2,2'-bipyridine) exhibit luminance and efficiency surpassing previous copper(I)-containing LECs.
Members of the diazeniumdiolate class of natural compounds show potential for drug development because of their antifungal, antibacterial, antiviral, and antitumor activities. Yet, their biosynthesis has remained elusive to date. Here, we identify a gene cluster directing the biosynthesis of the diazeniumdiolate compound fragin in Burkholderia cenocepacia H111. We provide evidence that fragin is a metallophore and that metal chelation is the molecular basis of its antifungal activity. A subset of the fragin biosynthetic genes is involved in the synthesis of a previously undescribed cell-to-cell signal molecule, valdiazen. RNA-Seq analyses reveal that valdiazen controls fragin biosynthesis and affects the expression of more than 100 genes. Homologs of the valdiazen biosynthesis genes are found in various bacteria, suggesting that valdiazen-like compounds may constitute a new class of signal molecules. We use structural information, in silico prediction of enzymatic functions and biochemical data to propose a biosynthesis route for fragin and valdiazen.
The complex [Ir(ppy) 2 (dpbpy)] [PF 6 ] (Hppy = 2-phenylpyridine, dpbpy = 6,6 0 -diphenyl-2,2 0 -bipyridine) has been prepared and evaluated as an electroluminescent component for light-emitting electrochemical cells (LECs); the complex exhibits two intramolecular face-to-face p-stacking interactions and long-lived LECs have been constructed; the device characteristics are not significantly improved in comparison to analogous LECs with 6-phenyl-2,2 0 -bipyridine.Light-emitting electrochemical cells (LECs) are a minimalist derivative of organic light-emitting devices (OLEDs) and in their simplest form consist of a film of an ionic transition metal complex placed between two electrodes. 1,2 LECs offer considerable technological advantages over OLEDs as they require a less reactive cathode material (Al instead of Ca or Mg) because the device is no longer dependent upon the work function of the electrode and hence do not require stringent protection from environmental oxygen or water. The disadvantage of LECs is the short operating lifetime, in the order of hours to days, compared to OLEDs. [3][4][5] We have recently reported the use of intra-and intermolecular face-to-face p-stacking for the stabilisation of the ground and excited state of electroluminescent iridium complexes and shown that this leads to exceptionally long-living LEC devices. 6,7 The long lifetimes of these devices establish LECs as a viable alternative to OLED technology. In [Ir(ppy)(pbpy)] + (Hppy = 2-phenylpyridine, pbpy = 6-phenyl-2,2 0 -bipyridine) the pendant phenyl group of the pbpy ligand forms a face-to-face p-stack with the metallated ring of a ppy ligand (3.2-3.5 Å ). This interaction minimises the expansion of the metal-ligand bonds in the excited state and precludes the attack by water and other nucleophiles resulting in the long observed lifetimes. We concluded that analogous complexes with 6,6 0 -diphenyl-2,2 0 -bipyridine would have an even greater stabilisation of the excited state as the two pendant phenyl groups would stack with different ppy ligands giving a very ''tight'' complex.The ligand 6,60 -diphenyl-2,2 0 -bipyridine, dpbpy, was obtained from the reaction of four equivalents of phenyllithium with 2,2 0 -bipyridine in THF followed by oxidation of the intermediate tetrahydro-species with MnO 2 according to the general procedure of Sauvage et al. ) and the complex is luminescent exhibiting an emission in MeCN solution with a maximum at 595 nm with a lifetime t = 0.6 ms and a quantum yield (PLQE) of 3%.We have determined the structure of [Ir(ppy) 2 (dpbpy)][PF 6 ]z and the [Ir(ppy) 2 (dpbpy)] + cation present in the lattice is shown in Fig. 1a. The Ir-N(ppy) (2.0504(17), 2.0341(17) Å ) and Ir-C(ppy) distances (2.0120 (18) . We stress here that the intramolecular p-stacking is a direct and inevitable consequence of the ligand structure and will be present in the solid state, solution and thin film phases. To summarise, as observed from the crystal structure, the use of the dpbpy ligand for optimising the
The electronic absorption spectra, luminescence spectra and lifetimes (in MeCN at room temperature and in frozen n-C3H7CN at 77 K), and electrochemical potentials (in MeCN) of the novel dinuclear [(tpy)Ru(3)Os(tpy)]4+ and trinuclear [(tpy)Ru(3)Os(3)Ru(tpy)]6- complexes (3 = 2,5-bis(2,2':6',2''-terpyridin-4-yl)thiophene) have been obtained and are compared with those of model mononuclear complexes and homometallic [(tpy)Ru(3)Ru(tpy)]4+, [(tpy)Os(3)Os(tpy)]4+ and [(tpy)Ru(3)Ru(3)Ru(tpy)]6+ Complexes. The bridging ligand 3 is nearly planar in the complexes, as seen from a preliminary X-ray determination of [(tpy)Ru(3)Ru(tpy)][PF6]4, and confers a high degree of rigidity upon the polynuclear species. The trinuclear species are rod-shaped with a distance of about 3 nm between the terminal metal centres. For the polynuclear complexes, the spectroscopic and electrochemical data are in accord with a significant intermetal interaction. All of the complexes are luminescent (phi in the range 10(-4)-10(-2) and tau in the range 6-340 ns, at room temperature), and ruthenium- or osmium-based luminescence properties can be identified. Due to the excited state properties of the various components and to the geometric and electronic properties of the bridge, Ru --> Os directional transfer of excitation energy takes place in the complexes [(tpy)Ru(3)Os(tpy)]4+ (end-to-end) and [(tpy)Ru(3)Os(3)Ru(tpy)]6+ (periphery-to-centre). With respect to the homometallic case, for [(tpy)Ru(3)Os(3)Ru(tpy)]6+ excitation trapping at the central position is accompanied by a fivefold enhancement of luminescence intensity.
A new iridium(III) complex showing intramolecular interligand pi-stacking has been synthesized and used to improve the stability of single-component, solid-state light-emitting electrochemical cell (LEC) devices. The pi-stacking results in the formation of a very stable supramolecularly caged complex. LECs using this complex show extraordinary stabilities (estimated lifetime of 600 h) and luminance values (average luminance of 230 cd m-2) indicating the path toward stable ionic complexes for use in LECs reaching stabilities required for practical applications.
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